When coding the pNFS server, I added several vn_start_write() calls done while the vnode was locked, not realizing I had introduced LORs and possible deadlock when an exported file system on the MDS is suspended. This patch fixes this by removing the added vn_start_write() calls and modifying the code so that the extant vn_start_write() call before the NFS RPC/operation is done when needed by the pNFS server. Flags are changed so that LayoutCommit and LayoutReturn now get a vn_start_write() done for them. When the pNFS server is enabled, the code now also changes the flags for Getattr, so that the vn_start_write() is done for Getattr, since it may need to do a vn_set_extattr(). The nfs_writerpc flag array was made global to the NFS server and renamed nfsrv_writerpc, which is consistent naming for globals in the NFS server. Thanks go to kib@ for reporting that doing vn_start_write() while the vnode is locked results in a LOR. This patch only affects the behaviour of the pNFS server.
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